1. Field of the Invention
The present invention relates to a toner replenishing device of a developing device used for an image forming device of an electro-photographic system, in particular, for a printer, a facsimile device, or a copier using a binary or a mono-component developer.
2. Description of the Background Art
Hard bottles have been conventionally used as storing vessels for dry toner, a carrier, or a mixture of the toner and carrier (hereafter referred to as toner) used for electrophotography in general. As the conventional toner replenishing devices, one in which a toner agitator-cum-discharge device is provided in the vessel, one which moves the toner in the vessel by rotating the vessel by providing a spiral groove on the vessel wall to discharge the toner, or one which has no discharge mechanism and is manually replenished with the toner, are known. In recent years, however, recovery or recyclability of the toner storing vessel is requested by attaching greater importance to the environmental problem.
Therefore, volume-reducible soft vessels made of flexible materials are proposed, as disclosed in the Japanese Patent Laid-Open Publication, for example, No. 2001-324863 or No. 2002-072649. The dry toner for electrophotograpy is, however, considered very difficult to be discharged from the soft vessel, since it has poor fluidity in general, and is liable to coagulate. This is because an agitator or a discharge mechanism is difficult to be added to the soft vessel, or addition of the discharge mechanism prevents volume reduction, or handleability is poor for manual replenishing.
The toner in the flexible vessel may be sucked and discharged by a sucking type powder pump, or a single-shaft eccentric screw pump, and the volume of the toner vessel may be reduced following toner discharge. Since an automatic volume-reduction type toner carrying apparatus carries the toner by a suction pressure (negative pressure) of the powder pump, carrying volume of the toner varies unless the suction pressure is constant, and the volume of the vessel cannot be gradually reduced. With a constant one-operation time of the powder pump, the pressure generated is constant, however, according to the state of the toner, for example, fluctuation of the toner characteristics due to the environment, or due to storing for a long period, a problem of variation of the suction pressure necessary for carrying the toner occurs.